Multi-trip annular seal repair method and associated equipment

ABSTRACT

A multi-trip method of repairing a leaking annular seal located within an annulus that encircles an oil/gas wellbore tubular body, examples of such seals including annular packers or cement seals. The method comprises providing deflector within a wellbore tubular body adjacent to one or more openings in the wall of the tubular body. Alloy beads are then deployed downhole via the tubular body so that the alloy beads are deflected via said openings into the annulus where they accumulate on top of the annular seal. A heating tool is then operated to heat the alloy within the annulus to form an alloy plug above the annular seal. The present invention also provides various pieces of downhole equipment for use in the repair method of the invention.

FIELD OF THE INVENTION

The present invention relates to the technical field of downhole operations in oil/gas wellbores, and in particular to remedial operations associated with repairing faults in annular seals, such as annular packers and cement seals, found within oil/gas wellbores.

BACKGROUND OF THE INVENTION

In order to access oil and gas deposits located in underground formations it is necessary to drill bore holes into these underground formations and deploy production tubing to facilitate the extraction of the oil and gas deposits.

Additional tubing, in the form of well lining or well casing, may also be deployed in locations where the underground formation is unstable and needs to be held back to maintain the integrity of the oil/gas well.

During the formation and completion of an oil/gas well it is crucial to seal the annular space created between the casing and the surrounding formation. Also the annular space between the different sizes casings used as the well is completed. Additionally the annular space between the production tubing and said casing needs to be sealed. Further seals may be required between the underground formation and the additional tubing.

One of the most common approaches to sealing oil/gas wells is to pump cement into the annular spaces around the casing. The cement hardens to provide a seal which helps ensure that the casing provides the only access to the underground oil and gas deposits. This is crucial for both the efficient operation of the well and controlling any undesirable leakage from the well during or after the well is operated.

However it is not uncommon for crack/gaps (sometime referred to as micro annuli) to form in these cement seals over time, which lead to unwanted leakage from the well. One location where such cracks/gaps can form is at the interface between the production tubing and the cement seal.

Another commonly used operation in oil/gas wells is the installation of packers to seal off zones within an annulus of a wellbore. However, as with cemented annuli, overtime annular packers can develop leaks.

In the case of repairing crack/gaps in the cement seal it is known to deploy eutectic alloy, such as bismuth alloy, into the annular space and then heat the alloy to so that it melts and flows into the cracks/gaps. The alloy is then allowed to cool, wherein it expands to form an effective seal. This process is described in International application WO 0194741 A1.

However there are disadvantages to this approach, not least because it requires at least a partial dismantling of the well so that the alloy can be deployed within the annular space, which can be time consuming and costly in terms of the down time of the well.

SUMMARY OF THE INVENTION

The present invention seeks to provide an alternative approach to repairing leaks that may have developed in an existing annular seal that is located in an annular space encircling a tubular body within an oil/gas wellbore. Typical annular seals include cement seals and annular packers.

In a first aspect of the present invention there is provided a method of repairing a leaking annular seal located within an annulus that encircles an oil/gas wellbore tubular body, said method comprising: positioning a deflector in a downhole target region within the tubular body so that the deflector is up-hole of the annular seal and down-hole of a portion of the tubular body wall that comprises one or more openings; delivering alloy beads to the downhole target region via the tubular body such that the deflector redirects the alloy beads radially outwards towards said one or more openings and into the annulus, wherein the alloy beads accumulate on top of the annular seal; and providing a heating tool comprising at least one heater within the wellbore tubular body at a location proximal to the annular seal and operating the heating tool to increase the temperature within the downhole target region to a temperature that is sufficient to melt the alloy beads accumulated within the annulus before allowing the molten alloy to cool and form a plug that repairs the leaking annular seal.

Preferably the annular seal being repaired may comprise an annular packer and/or a cement seal.

It will be appreciated that the terms ‘up-hole’ and ‘down-hole’ used herein are intended to denote the relative positioning of the various elements present in the wellbore. That is to say, ‘up-hole’ denotes that a first element is closer to the surface of the wellbore than a second element, (i.e. the first element is located between the surface and the second element).

Conversely, ‘down-hole’ denotes that the first element is further away from the surface of the wellbore than the second element (i.e. the second element is located between the surface and the first element).

Rather than deploying the alloy downhole from the surface of the wellbore via the annulus that houses the annular seal that is to be repaired, the method of the present invention utilises the innermost wellbore tubular body to achieve the majority of the alloy's journey to a downhole target region. In this way it is possible to make use of the cleaner internal diameter of the innermost tubular body, which typically has less restrictions than the annulus not least due to the absence of couplings that project into the annulus.

In the case of couplings, which occur at the points when consecutive well tubulars are joined, alloy beads that are deployed down the annulus can land on the upper surfaces of the couplings and in so doing be prevented from reaching the downhole target region. The loss of alloy beads in transit due to obstructions within the annulus can be significant over the full distance from the surface to the target region.

It is only once the alloy reaches the vicinity of the up-hole face of the annular seal (i.e. the downhole target region), that is to say the face of the annular seal that is closest to the surface of the wellbore, that the alloy passes into the annulus.

The passage of the alloy (which is provided in the form of beads, balls or shot) through the wall of the innermost tubular body into the annulus is achieved via one or more openings provided in the tubular body at a location that is up-hole of the annular seal.

It is envisioned that in the broadest applications of the method of the invention the passage of the alloy beads through the tubular body is achieved via pre-existing openings. Examples of pre-existing openings include valves, such as: sliding sleeve valves, gas lift mandrel valves, and pressure diverter subs. With that said it is also envisioned that in those situations where there are no suitable pre-existing openings, hole making equipment may be employed to create one or more openings in the tubular body.

In order to direct the alloy beads from within the tubular body to the annulus via said one or more openings, the method employs a deflector that is also delivered downhole via the tubular body to a location that is down-hole of said one or more openings.

The positioning and configuration of the deflector is such that when the alloy beads are deployed within the tubular body they contact the deflector and are redirected radially outwards towards said one or more openings and out into the annulus, wherein the alloy beads accumulate on top of the up-hole face of the annular seal.

A heating tool, which is also deployed downhole via the tubular body, is operated to increase the temperature within the target region to a level that is sufficient to melt the alloy beads. Following the operation of the heating tool the molten alloy is allowed to cool, wherein the alloy solidifies within the annulus as an alloy plug that effectively repairs any leaks within the annular seal.

Although the heating tool can be deployed to any location that is within heating range of the up-hole face of the annular seal, preferably said heating tool is deployed to a location within the wellbore tubular body that is proximal to and up-hole of the annular seal.

Preferably the heating tool comprises multiple heaters that are operated independently to provide heat at different times. This use of multiple, independently controllable heaters provides the operator with much greater control of the heating levels within the downhole target region.

Further preferably, said heaters are independently operated to: a) commence generating heat before the heating tool reaches the downhole target region; b) pre-heat the alloy beads before they are redirected into the annulus by the deflector; c) pre-heat the downhole target region before the alloy beads are accumulated on top of the annular seal; d) provide the alloy melting temperature within the downhole target region after the alloy beads have begun to accumulate on top of the annular seal; and/or e) provide the alloy melting temperature within the downhole target region once the alloy beads have accumulated on top of the annular seal.

Preferably the step of positioning the deflector in the downhole target region may comprise deploying a bridge plug assembly within the wellbore tubular body, said bridge plug assembly being provided with the deflector on an up-hole face thereof.

Further preferably the bridge plug assembly may be deployed using a delivery support that is connected to delivery means located above-ground at the surface of the wellbore.

Preferably the heating tool may be deployed using a delivery support that is connected to delivery means located above-ground at the surface of the wellbore.

Further preferably the heating tool may further comprise a baffle configured to be positionable in the wellbore tubular body at a location between the heating tool and the delivery means, said baffle being configured to restrict the movement of heating fluids produced during the operation of the heating tool.

In those embodiments where the heating tool comprises a baffle, it is considered preferable that the baffle is configured to also function as an alloy bead deflector.

With respect to the bridge plug assembly and/or the heating tool, the delivery support is preferably selected from: coiled tubing, pipe, slick line and wireline.

Preferably the delivery of the alloy beads may be achieved by dumping the alloy beads into the wellbore tubular body from above-ground at the surface of the wellbore.

Alternatively the delivery of the alloy beads may be achieved by a dump bailer deployed downhole via the tubular body. Further preferably the alloy may be delivered from a dump bailer that forms part of the bridge plug assembly and/or the heating tool. However, the dump bailer may also be delivered downhole separately.

In a further alternative, the delivery of the alloy beads may be achieved via the coiled tubing or pipe that is used to deploy the bridge plug assembly and/or the heating tool assembly.

As noted above, in its broadest application the method of the present invention makes use of pre-existing openings in the well bore tubular body to facilitate the passage of the alloy beads from within the tubular body to the surrounding annulus.

However, in situations where there are either no pre-existing openings in the wall of the tubular body, or the pre-existing openings are unsuitable to enable the passage of the alloy beads, the method may preferably further comprise forming one or more openings in the portion of the tubular body wall that is located up-hole from the annular seal.

Preferably said one or more openings may be formed using hole making equipment, wherein the hole making equipment is selected from: a drill, a mechanical punch, a perforating gun, a saw or any other suitable cutting tools such as chemical cutters and fluid jet cutters.

Preferably said one or more openings may be formed in the tubular body wall before the deflector is positioned within the downhole target region.

Preferably the downhole target region may be agitated in order to assist the passage of the alloy beads through said one or more openings into the annulus.

It will be appreciated that although the suitable openings will be big enough to allow the alloy beads to pass through the wall of the tubular body, when large amounts of alloy beads are deployed at once blockages may occur. Agitating the downhole target region will help to shake the alloy beads through openings so that they can reach the surrounding annulus.

Preferably the deflector is vibrated to agitate the downhole target region. Additionally, or alternatively, the tubular body is vibrated to agitate the downhole target region. Employing either agitation approach, or indeed a combination of these approaches at the same time, helps to prevent the build-up of the alloy beads on the inside of the tubular body.

It is envisioned that the agitation of the downhole target region may be achieved by a motor assembly deployed downhole after the deflector has been positioned in the target region.

It is envisioned that in those embodiments where a deflector and a heating tool are present within the wellbore at the same time, the deflector will also act to reduce the flow of heating fluids upwards within the tubular body and in so doing reduce the amount of heat being lost from the downhole target region. Reducing heat loss in this way also helps to make more efficient use of the heating tool.

With that said, preferably the deflector may comprise insulating means configured to restrict the passage of conducted heat through the deflector. In this way the deflector not only acts to reduce the amount of heat lost as a result of heated fluids rising within the tubular body, but is also prevents heat being transferred across the deflector via a process of conduction.

Preferably the deflector may be deployed downhole in an unexpanded or partially expanded state and then expanded towards the tubular body wall in the downhole target region so as to increase the extent to which the deflector redirects the alloy beads. It is appreciated that expanding the deflector in this way will also further restrict the upward flow of heating fluids within the wellbore.

In this way the deflector is easier to deliver downhole in situations of restricted access (e.g. when the tubular body is of smaller diameter and/or the tubular body has one or more obstructions within it).

Preferably the method further comprises the intermediate step of retrieving the deflector after the alloy beads have been delivered but before the heating tool is provided within the tubular body and operated.

Preferably the method further comprises the step of deploying a junk basket downhole via the wellbore tubular body to a position that is down-hole of the downhole target region. In this way alloy beads that fall past the deflector are prevented from falling further by the junk basket.

Further preferably the junk basket may be delivered downhole in combination with the bridge plug assembly or the heating tool or indeed on its own.

It is envisaged that this approach involves multiple deployments (i.e. multiple trips) down the wellbore, however this allows for each stage of the repair method to be completed by a tool specific to that function (i.e. wellbore tubular body perforation, alloy bead deflection, and alloy bead melting). This may be advantageous in situations where a larger heating tool is required to achieve the desired melting of the alloy beads within the annulus, for example.

Preferably the heating tool comprises one or more chemical reaction heaters. The chemical reaction heaters preferably employ thermite or thermite based mixes for the generation of heat that is suitable to melt the alloy beads.

Preferably the alloy beads are provided in the form of a low melting alloy that has melting point of less than 300° C. These low melting alloys are sometimes also referred to as fusible alloys. With that said, it will be appreciated that in order for the alloy to be capable of forming a solid alloy plug within the annulus the melting point of the alloy must not be lower than the normal temperature in the downhole target region, which is typically 5 to 50° C.

Preferably the alloy beads may be provided in the form of bismuth based alloys. It is envisioned that the bismuth based alloys may be eutectic or non-eutectic in nature and may also qualify as low melting alloys.

In addition to the packer repair method of the first aspect of the present invention, a second aspect of the present invention provides a bridge plug assembly for use in the annular seal repair method of the present invention.

Accordingly, the present invention provides a bridge plug assembly for use in forming an alloy plug on an existing annular seal that encircles an oil/gas wellbore tubular body, said assembly comprising: a bridge plug operable to expand against and engage with the wellbore tubular body such that the bridge plug is retained in position within the wellbore tubular body; and a deflector configured to obstruct alloy beads delivered downhole and redirect them radially outwards towards the tubular body wall, wherein the deflector is arranged up-hole of the bridge plug.

It is envisioned that the assembly can be used to carry out the alloy bead delivery stage of the annular seal repair method of the present invention in a multi-trip approach.

Preferably the bridge plug assembly may further comprise a delivery support connection point, by which the assembly is connectable to delivery means via a delivery support such that said assembly can be delivered to and retrieved from a downhole target region of a wellbore tubular body.

Further preferably the assembly may comprise a delivery support connected to the delivery support connection point and wherein the deflector is located on the delivery support; wherein preferably the delivery support is selected from: coiled tubing, pipe, slick line and wireline.

Preferably the deflector may comprise an up-hole facing surface that comprises at least one sloped region. In this way, when the alloy beads hit the deflector they are re-directed radially outwards towards the wall of the tubular body in which said one or more openings are located.

Further preferably the up-hole facing surface of the deflector is cone-shaped or domed. Further, the apex of the cone or the dome is preferably located on a central axis running through the deflector.

Additionally or alternatively the deflector may comprise an agitation mechanism configured to vibrate the deflector. As detailed above, agitating the deflector helps to prevent the alloy beads from becoming jammed in said one or more openings in the tubular body wall, which would otherwise prevent the alloy beads from passing through into the annulus.

Preferably the deflector may be configured to be expandable radially outwards towards the tubular body wall. In this way the deflector can be delivered downhole in a smaller form and then, once in position, increased in size to make it more effective at re-directing the alloy beads.

Further preferably the mechanism by which the expansion of the deflector is achieved is selected from hydraulic means, pneumatic means, mechanical means and combinations thereof.

In particular, in the case of a mechanical expansion means, the deflector may preferably be urged to expand and/or contract by way of one or more resilient biasing means. Further preferably the deflector may comprise a canopy of flexible material connected to an umbrella spring mechanism.

Preferably the deflector may comprise insulating means configured to restrict the passage of conducted heat through the deflector. As detailed above, providing the deflector with insulating properties helps to reduce the amount of heat lost from the downhole target region. This in turn helps to make more efficient use of the heat generated by the heating tool.

Preferably the assembly may further comprise a junk basket positioned at the leading end of the assembly. In this way, any material that may fall down hole from the downhole target region when the bridge plug is retrieved can be caught.

A third aspect of the present invention provides a downhole heating assembly for use in the annular seal repair method of the present invention.

Accordingly, the present invention provides a downhole heating assembly comprising: a heating tool with at least one heater; a delivery support connection point, by which the heating tool is connectable to delivery means via a delivery support such that said heating assembly can be delivered to and retrieved from a downhole target region of a wellbore tubular body; and a baffle configured to be positionable in the wellbore tubular body at a location between said heating tool and said delivery means, said baffle being configured to restrict the movement of heated fluids produced during the operation of the heating tool.

It is envisioned that the assembly can be used to melt the alloy beads within the annulus during the plug formation stage of the annular seal repair method of the present invention in a multi-trip approach.

Preferably the baffle may be located between the heating tool and the delivery support connection point.

Preferably the assembly may further comprise a delivery support connected to the delivery support connection point and wherein the baffle is located on the delivery support. Further preferably the delivery support may be selected from: coiled tubing, pipe, slick line and wireline.

Preferably the baffle may be configured to be expandable towards the walls of a wellbore tubular body so as to increase the extent to which the baffle restricts fluid movement within the wellbore.

Further preferably the mechanism by which the expansion of the baffle is achieved may be selected from hydraulic means, pneumatic means, mechanical means and combinations thereof.

Preferably the assembly may comprise control means that co-ordinate the operation of the heating tool and the expansion of the baffle.

Preferably the control means that control the expansion of the baffle may be provided on the heating tool.

Preferably the baffle may be urged to expand and/or contract by way of one or more resilient biasing means. Further preferably the baffle may comprise a canopy of flexible material connected to an umbrella spring mechanism.

Preferably the baffle may be positioned a distance of up to 6 m (approx. 20 feet) from the heating tool, and further preferably between 0.3 to 1.0 m (approx. 1 to 3 feet).

Preferably the baffle may be configured to function as a deflector.

Preferably the heating tool may comprise one or more chemical reaction heaters. The chemical reaction heaters preferably employ thermite or thermite based mixes for the generation of heat that is suitable to melt the alloy beads.

Preferably the baffle may comprise insulating means configured to restrict the passage of conducted heat through the baffle. Providing the baffle with insulating properties helps to reduce the amount of heat lost from the downhole target region. This in turn helps to make more efficient use of the heat generated by the heating tool.

Preferably the assembly may further comprise a junk basket positioned at the leading end of the assembly. In this way, any material (e.g. alloy beads) that may fall down hole from the downhole target region can be caught.

BRIEF DESCRIPTION OF THE DRAWINGS

The various aspects of the present invention will now be described with reference to the preferred embodiments shown in the drawings, wherein:

FIG. 1 shows a diagrammatic representation of the key stages of an annular seal repair method according to a first preferred embodiment of the present invention;

FIG. 2 shows a diagrammatic representation of the key stages of an annular seal repair method according to a second preferred embodiment of the present invention;

FIG. 3 shows a diagrammatic representation of the key stages of an annular seal repair method according to a third preferred embodiment of the present invention;

FIG. 4 shows a diagrammatic representation of the key stages of an annular seal repair method according to a fourth preferred embodiment of the present invention; and

FIG. 5 shows a preferred embodiment of a deflector used in the heating tool assembly of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The annular seal repair method of the present invention will now be described with reference to the various preferred embodiments shown in the figures.

It should be appreciated from the outset that assemblies shown in the figures are not intended to be limiting, but rather to demonstrate examples of how certain preferred components work in combination with the essential components of the heating tool and the deflector to help repair an annular seal, such as an annular packer.

FIG. 1 shows the application of the annular seal repair method of the present invention in a wellbore target region where only a single annulus is present. The annulus 3 is defined by the outer casing 1 and the inner tubular body 2. Within the annulus 3 is provided an annular packer 4. The annular packer 4 shown in FIG. 1 has a fault line which is causing the packer 4 to leak, hence the application of the annular seal repair method.

In the first stage of the method shown in FIG. 1 a junk basket assembly 5 is deployed downhole to a location that is down hole of the target region of the annular seal repair. The junk basket assembly 5 comprises a bridge plug 6 with a junk basket 7 provided on its up-hole face. Once in position, the bridge plug is actuated to set it in place within the wellbore tubular body 2.

The junk basket assembly 5 is deployed downhole using a common delivery support that is connected to delivery means located above-ground at the surface of the wellbore.

The delivery means are not shown in FIG. 1 , but it will be appreciated by the skilled person that standard delivery means can be utilised to achieve the deployment of the junk basket assembly 5.

Also, although the delivery support is not shown in any detail, it will be appreciated that suitable types of delivery support include coiled tubing, pipe, slick line and wireline. It is appreciated that any combination of delivery support and delivery means can be employed provided it facilitates the controlled deployment of the junk basket assembly 6 to the downhole target region via the interior of the tubular body 2.

Following the deployment of the junk basket assembly 5, a perforating tool 8 is deployed downhole via the inner diameter of the tubular body 2. As with the junk basket assembly 5, although not shown in detail, is appreciated that any combination of delivery support and delivery means can be employed to deliver the perforating tool downhole.

Using the perforating tool 8, one or more openings 9 are formed in a portion of the wellbore tubular body 2 that is located up hole of the annular seal 4. It is envisioned alternative hole making equipment could be employed to produce said openings 9; examples of which include: a drill, a mechanical punch, a perforating gun, a saw or any other suitable cutting tools such as chemical cutters and fluid jet cutters.

Following the formation of the openings 9, the perforating tool 8 is retrieved and a bridge plug assembly 10 is delivered downhole and set in a location that is proximal to, but down-hole of, the openings 9.

Once the bridge plug assembly 10 is in position within the downhole target region, alloy beads 11 are delivered to the downhole target region. In the preferred embodiment shown in FIG. 1 the alloy beads are delivered by a process of dumping the alloy beads into the wellbore tubular body 2 at the surface of the wellbore above ground (not shown).

The dumped alloy beads 11 fall down the wellbore via the inner tubular body until they come into contact with the up-hole face of the bridge plug assembly 10, which acts as a deflector and re-directs the alloy beads 11 radially outward towards the openings 5 in the wellbore tubular body 2 and out into the annulus 3. The alloy beads 9 then accumulate on the up-hole surface of the annular packer 4.

Although not shown it is envisaged that, following the delivery of the alloy beads onto the bridge plug assembly 10, agitation means may be deployed to agitate any alloy beads that may remain on the up-hole surface of the bridge plug assembly 10. The agitation means may act to vibrate alloy beads either directly or indirectly, by vibrating the tubular body 2 at location that is up-hole of the target region.

It is envisaged that in those embodiments where the tubular body 2 is vibrated, the agitation means may be operated at a distance away from the annular seal because of the greater freedom of movement available to the portion of the tubular body that is not restricted by the annular seal. The agitation means may comprise a motor assembly with a weight mounted on an axle with an offset arrangement, such that the rotation of the weight about the axle generates a vibrating force.

Once the alloy beads 11 have been delivered into the annulus and onto the annular seal 4, the bridge plug assembly 10 is then retrieved from the wellbore in a process that is a reverse of the assembly's delivery.

It is envisaged that when the bridge plug assembly 10 is retrieved any alloy beads retained on the up-hole surface of thereof may fall downhole. However the presence of the junk basket assembly 5 ensures that these alloy beads 11 are captured for later retrieval.

In the broadest sense of the present invention the alloy beads can be formed from any alloy, provided the alloy melts at a temperature above that found within the downhole environment (e.g. around 5 to 50° C.). This is important because it enables the alloy form a stable solid plug within the annulus.

Preferably, however, the alloy beads 11 are formed from a low melting alloy that has a melting point that is no more than about 300° C. and which further preferably comprises bismuth. Bismuth is preferred component because it its alloys tend to contract upon melting and expand upon re-solidification, which is considered beneficial when forming alloy plugs.

Typically the alloy beads will have a diameter in the range of 0.76 to 127 mm (about 0.030 to 0.5 inches). However, ultimately the size of the beads will be determined by the openings in the tubular body wall and any other restrictions that might exist because the alloy beads must be able to pass downhole and through the openings into the annulus with relative freedom.

Following the retrieval of the bridge plug assembly 10, a heating tool 12 is delivered downhole via the inner diameter of the wellbore tubular body 2. Once again, although not shown in detail, is appreciated that any combination of delivery support and delivery means can be employed to deliver the heating tool 12 downhole.

Although the heating tool 12 shown in FIG. 1 comprises only a single heater, it is envisaged that the heating tool 12 may comprise multiple individually operable heaters. Employing multiple heaters in this way provides the option to operate the heaters sequentially or in unison to achieve different heating programs.

For example, one possible heating program might employ a first heater to preheat but not necessarily melt the alloy beads. A second heater could then be operated to ensure complete melting of the alloy. This is considered particularly beneficial in the downhole environments where there is a significant difference between the ambient temperature in the target region and the melting point of the alloy.

However, in the embodiment shown the heating tool 12 comprises a single heater that is operated once the whole load of alloy beads 11 have been delivered to the annulus 3. Preferably the heating tool comprises at least one chemical heater that generates heat from a thermite based reaction. With that said, alternative heat sources will be appreciated by the skilled person.

Once the alloy beads have been heated for a suitable length of time (for example 2 hours) the molten alloy is allowed to cool and as it does the alloy re-solidifies on top of the existing annular packer 4 to form a plug 13, which acts to seal any fissures/cracks in the packer.

Once the alloy beads have been sufficiently melted the heating tool 12 can be retrieved from the wellbore using the common delivery support and the above-ground delivery means.

In the final stage of the method shown in FIG. 1 the junk basket assembly 5 is retrieved.

Turning now to FIG. 2 , a second preferred embodiment of the method of the present invention will now be described. The first two stages of this repair method are the same as shown in FIG. 1 and as such will not be described an any further detail here.

In the third stage, however, rather than deploying a bridge plug assembly the method of this embodiment involves the delivery of a heating tool assembly 15 to the downhole target region. The heating tool assembly 15 comprises a heating tool 16 with a deflecting baffle 17 mounted up-hole thereof.

The heating tool assembly 15 is position within the wellbore tubular body such that the deflecting baffle 17 is positioned proximal to but down-hole of the openings 9. The deflecting baffle 17 is shown in an expanded state wherein the majority of the inner diameter of the tubular body 2 is occluded.

It is envisioned that the expansion of the deflecting baffle 17 can be achieved by way of hydraulic means, pneumatic means, mechanical means and combinations thereof.

It is appreciated that deploying the heating tool assembly 15 downhole with the deflecting baffle 17 in an unexpanded or partially expanded state helps to make the assembly's passage easier, particularly in wellbore tubular bodies of limited diameter and/or which contain obstructions. Reducing the size of deflecting baffle 17 during transit also reduces the resistance due to the existing wellbore fluids by allowing some flow area for the fluid to pass the deflecting baffle 17.

In the embodiment shown in FIG. 2 it can be seen that the deflecting baffle 17 has an upper face that is dome-shaped such that alloy beads striking the deflecting baffle are re-directed radially outward.

As a general point it is noted that the upper surface of the deflectors employed in the present invention, including the deflecting baffle 17 shown in FIG. 2 , may comprise different shapes, ranging from cone-shaped to single flat sloped faces, and that any face shapes that help re-direct the alloy beads towards the tubular body wall are preferable.

With that said, it is not considered essential for the upper face of the deflector to be sloped because the process of re-directing the alloy beads towards the wall of the tubular body could also be achieved by agitating the downhole target region to help shake the alloy beads through the openings and into the annulus; as per the embodiment shown in FIG. 1 .

With the heating tool assembly 15 in position, the alloy beads 11 are delivered to the downhole target region via the tubular body 2. As before, the alloy beads 11 are dumped downhole from dumping means located at the surface of the wellbore.

Once again the alloy beads 11 descend the wellbore within the tubular body and those that strike the deflecting baffle 17 are re-directed towards the openings 9 and out into the annulus 3, where they accumulate on the up-hole face of the annular packer 4.

Any of the alloy beads 11 that miss the deflecting baffle continue to descend past the heating tool 16. In such situations the alloy beads 11 that are not redirected into the annulus 3 are caught by the junk basket 7 located down-hole of the heating tool assembly 15.

As in the method of the first embodiment described above, the heating tool 16 is operated to heat the downhole target region to a temperature that is sufficient to melt the alloy beads 11.

Further, it is envisaged that the deflecting baffle 17 may comprise heat insulating means that are configured to minimise the passage of heat therethrough. In this way the deflecting baffle serves a dual purpose of achieving alloy bead re-direction and also lowering the amount of heat lost from the downhole target region due to the upward flow of heated wellbore fluids.

In particular, it is noted that by at least partially occluding the tubular body 2 with the deflecting baffle 17 it is possible to reduce the extent to which fluids heated by the operation of the heating tool are lost up-hole. In this way heat is retained locally and the overall efficiency of the heating tool is improved.

Although this benefit is achieved to a greater or lesser extent by all of the deflectors employed in the method of the present invention, it is also appreciated that further heat retaining benefits may be achieved by providing the deflector with heat insulating means. In this way heat lost by conduction through the deflector is also reduced. In view of this it is envisaged that suitable heat insulation means could be employed in any of the deflectors shown in the preferred embodiments described herein.

Once melted, the alloy beads are allowed to cool and re-solidify to form an alloy plug 13 within the annulus 3, which sits on top of the annular packer 4 and seals any leaks therein.

The heating tool assembly 11 and the junk basket assembly 5 can then be retrieved in turn from the wellbore using the above-ground delivery means.

FIG. 3 shows a third preferred embodiment of the method of the present invention. In contrast to the situations shown in FIGS. 1 and 2 , there are pre-existing openings 9 in the tubular body 2 wall. It is envisioned that the pre-existing holes may be the result of a previous downhole operation or could be provided by components already present on the tubular body 2; such as valves (e.g. sliding sleeve valves, gas lift mandrel valves, and pressure diverter subs).

In the first stage a deflector assembly 20, which comprises an expandable deflector 21 with a junk basket 22 hanging down from it, is delivered downhole and positioned such that the deflector is proximal to but down-hole of the pre-existing opening 9 in the wall of the tubular body 2.

As described above, delivering the deflector 21 downhole in a partially expanded or unexpanded state facilitates an easier passage down the inner diameter of the tubular body 2.

Additionally the junk basket 22 is also expandable and so it too can be delivered downhole in a partially expanded or unexpanded state to again ease the passage of the deflector assembly 20 downhole. As before, it is envisioned that the expansion of the deflector 21 and the junk basket 22 can be achieved by way of hydraulic means, pneumatic means, mechanical means and combinations thereof.

Once the assembly 20 is in place, and the deflector 21 and junk basket 22 have been expanded, alloy beads 11 are delivered to the downhole target region. Once again the alloy beads 11 are delivered by a process of dumping the alloy beads into the wellbore tubular body 2 at the surface of the wellbore above ground (not shown).

The dumped alloy beads 11 fall down the wellbore via the inner tubular body 2 until they come into contact with the deflector 21, at which point they are re-directed radially outward towards the openings 9 in the wellbore tubular body 2 and out into the annulus 3. The alloy beads 11 then accumulate on the up-hole surface of the annular packer 4. Any alloy beads 11 that are not successfully re-directed by the deflector 21 can be caught in the junk basket 22.

Once the alloy beads 11 have been delivered into the annulus 3, and the deflector assembly 20 has been retrieved, a heating tool 23 is delivered to the downhole target region via the wellbore tubular body 2. Upon activation the heating tool 23, which is preferably a chemical heater with a thermite based reaction heat source, increases the temperature within the target region to a level that is sufficient to melt the alloy beads 11 within the annulus.

Once the alloy beads have been sufficiently melted the heating tool 23 can be retrieved from the wellbore using the common delivery support and the above-ground delivery means.

As the alloy cools it will resolidify and form a plug 13 over the annular packer 4, thereby effecting a repair within the annulus.

FIG. 4 shows a further preferred embodiment of the annular seal repair method of the present invention. The downhole target region shown in FIG. 4 comprises two annuli. The first annulus is defined by the outer casing 1 and the intermediate well tubing 2 a and the second annulus 3 is defined by the intermediate well tubing 2 a and the wellbore tubular body 2. In this shown example the failing annular packer 4 is provided in the second annulus.

The key stages shown in FIG. 4 are similar to those shown in FIG. 1 , albeit without the initial step of deploying a junk basket within the tubular body 2 at a point below the downhole target region. With that said, it is envisaged that a junk basket assembly delivery step could be included without departing from the overall scope of the present invention.

In the first stage shown in FIG. 4 a piece of hole making equipment is delivered downhole and operated to form one or more openings 9 in a portion of the tubular body 2 wall that is located up-hole of the annular packer 4. Again, preferably the hole making equipment used is a perforating tool 8. However the skilled person will appreciate that other types of hole making equipment could be suitably employed for this step.

Following the formation of the openings 9 the perforating tool 8 is retrieved and a bridge plug assembly 10 is set in place within the downhole target region at a location that is proximal to but down-hole of the openings 9. Once the bridge plug assembly 10 is set, a dump bailer 24 loaded with alloy beads 11 is delivered downhole via the tubular body 2.

Once it is in position above the bridge plug assembly 10 the dump bailer is operated to release the alloy beads onto the up-hole surface of the bridge plug which acts as a deflector and re-directs the alloy beads 11 towards the openings 9 and into the annulus 3.

As described with respect to the repair method shown in FIG. 1 , agitation means (not shown) may also be employed to assist the process of re-directing the alloy beads 11 into the annulus 3.

With the alloy beads 11 in place on top of the annular packer 4 the bridge plug assembly 10 can be retrieved and a heating tool 23 can be delivered to the downhole target region. Once in position the heating tool 23 is operated to melt the alloy beads so that an alloy plug 13 can be formed.

Once the alloy beads have been melted the heating tool 23 can be retrieved from the wellbore.

The operation of the deflector will now be described with reference to Figure which shows a partial view of a preferred embodiment of the heating tool assembly 15 of the present invention in both an unexpanded state and an expanded state in which the deflecting baffle 17 extends beyond the outer diameter of the heating tool 16.

It will be appreciated that expansion mechanism of the deflecting baffle 17 described below could also be employed in the other expandable deflectors referred to herein and is not specifically limited to use in combination with a heating tool 16 in a heating tool assembly 15. In addition, the described expansion mechanism could also be employed in an inverted orientation to provide the expandable junk basket referred to above.

The heater 16, of which only the uppermost portion is shown, is provided with a setting tool 25 that essentially houses the control mechanisms for operating the heater (e.g. ignition means in the case of a chemical heater).

The setting tool is then connected via a delivery support connection point 26 to a delivery support, which is shown as a wireline 27 but could be any suitable connection line, pipe or coil. The deflector 17 is located between the connection point 26 and the setting tool 25 of the heater 16.

The deflector 17 comprises a central shaft 28 that is connected between the setting tool 25 of the heater 16 and the delivery support connection point 26. A collar 29 is fixed in position on the shaft 28. Attached to the collar 29 is a web of flexible material 30 that essentially forms a canopy that is capable of changing shape to accommodate the expansion and contraction of the deflector 17.

It will be appreciated that the flexible material should be resistant to the downhole environment within which the assembly 15 is to be deployed. It is envisaged that a suitable flexible material for use in the deflector is a heat resistant canvas or a silicone rubber. However the skilled person will appreciate that other flexible materials could suitably be employed.

The deflector 17 further comprises a plurality of resiliently biased expansion bands 32 that are secured at their respective ends to the connection point 26 and a moveable collar 31, which is slideably mounted on the central shaft 28. In this way the unsecured middle portions of the bands are free to bend and flex in a radial direction relative to the central shaft.

It is envisaged that the resiliently biased expansion bands 32 may be formed from flexible strips of a suitable spring metal. However the skilled person will appreciate that an alternative resilient material may be employed without departing from the scope of the present invention.

In the preferred embodiment the moveable collar 31 is urged away from the setting tool 25 by way of actuation means 33, which may take the form of a coiled spring. It is envisaged that the actuation means 33 can be used to control the distance between the connection point 25 and the collar 31, which in turn will control the extent to which the resiliently biased expansion bands 32 can be deformed.

In this regard the actuation means 33 can limit the extent to which the collar 31 can move up and down the central shaft, which in turn limits the extent to which deflector 17 can be expanded or contracted.

The central portion of the canopy of flexible material 30 is attached to the fixed collar 29 whilst the periphery of the canopy is attached to each of the plurality of resiliently biased expansion bands 32. By connecting the flexible material to the middle portions of the resiliently biased expansion bands 32, the deflector can be operated to expand and contract the flexible material so that the extent to which it can deflect the alloy beads is varied and also restrict the flow of fluid past the deflector.

When the resiliently biased expansion bands 32 are forced radially outwards they pull the flexible material outwards (shown as 30 a) to form an expanded blocking structure that may extend across a large portion, if not all, of the inner diameter of the wellbore tubular body. Also, when the resiliently biased expansion bands 32 move radially inwards they pull in the flexible material 30 and contract the deflector 17.

It is envisaged that preferably, at rest, the bands 32 will extend outwards beyond the outer diameter of the rest of the heater assembly 16 so that the canopy of flexible material will at least partially block the borehole and, in so doing, restrict the flow of fluids within the borehole.

However, the flexible nature of the bands allows the deflector to compress, as necessary, to accommodate narrowed portions of the borehole that might be encountered during the annular seal repair tool assembly's deployment. Once past the narrowed portion of a borehole, the resilient nature of the bands will cause the baffle to once again return to its expanded state, in which the deflector restricts the movement of alloy beads and fluid within the wellbore tubular body.

It is further envisaged that, in use, the canopy may be caused to expand even further under the influence of heated fluids rising within the borehole. That is rising fluid could become trapped by partially opened canopy and then urge it to open further.

In an alternative arrangement of the mechanical arrangement shown in Figure the actuation means 33 may be operated to force moveable collar 31 to slide up the shaft 28, thereby urging the resiliently biased expansion bands 32 outwards and opening the canopy.

It is envisaged that this arrangement could be employed in embodiments where the deflector's default position in the unexpanded state. 

1. A method of repairing a leaking annular seal located within an annulus that encircles an oil/gas wellbore tubular body, said method comprising: positioning a deflector in a downhole target region within the tubular body so that the deflector is up-hole of the annular seal and down-hole of a portion of the tubular body wall that comprises one or more openings; delivering alloy beads to the downhole target region via the tubular body such that the deflector redirects the alloy beads radially outwards towards said one or more openings and into the annulus, wherein the alloy beads accumulate on top of the annular seal; and providing a heating tool comprising at least one heater within the wellbore tubular body at a location proximal to the annular seal and operating the heating tool to increase the temperature within the downhole target region to a temperature that is sufficient to melt the alloy beads accumulated within the annulus before allowing the molten alloy to cool and form a plug that repairs the leaking annular seal.
 2. The method of claim 1, wherein the annular seal comprises a cement seal and/or an annular packer.
 3. The method of claim 1 or 2, wherein the heating tool is provided at a location within the wellbore tubular body that is proximal to and up-hole of the annular seal.
 4. The method of claim 1 or 2, wherein said heating tool comprises multiple heaters that are operated independently to provide heat at different times.
 5. The method of claim 4, wherein said heaters are independently operated to: a) commence generating heat before the heating tool reaches the downhole target region; b) pre-heat the alloy beads before they are redirected into the annulus by the deflector; c) pre-heat the downhole target region before the alloy beads are accumulated on top of the annular seal; d) provide the alloy melting temperature within the downhole target region after the alloy beads have begun to accumulate on top of the annular seal; and/or e) provide the alloy melting temperature within the downhole target region once the alloy beads have accumulated on top of the annular seal.
 6. The method of any one of the preceding claims, wherein the step of positioning the deflector in the downhole target region comprises deploying a bridge plug assembly within the wellbore tubular body, said bridge plug assembly being provided with the deflector on an up-hole face thereof.
 7. The method of claim 6, wherein the bridge plug assembly is deployed using a delivery support that is connected to delivery means located above-ground at the surface of the wellbore.
 8. The method of any one of the preceding claims, wherein the heating tool is deployed using a delivery support that is connected to delivery means located above-ground at the surface of the wellbore.
 9. The method of claim 8, wherein the heating tool further comprises a baffle configured to be positionable in the wellbore tubular body at a location between the heating tool and the delivery means, said baffle being configured to restrict the movement of heating fluids produced during the operation of the heating tool.
 10. The method of claim 9, wherein the baffle is employed as a deflector to redirect the alloy beads radially outwards towards said one or more openings and into the annulus.
 11. The method of claim 7, 8, 9 or 10, wherein the delivery support is selected from: coiled tubing, pipe, slick line and wireline.
 12. The method of any one of the preceding claims, wherein the delivery of the alloy beads is achieved by dumping the alloy beads into the wellbore tubular body from above-ground at the surface of the wellbore.
 13. The method of any one of claims 1 to 11, wherein the delivery of the alloy beads is achieved by a dump bailer deployed downhole via the tubular body.
 14. The method of claim 13, wherein the alloy is delivered from a dump bailer that forms part of the bridge plug assembly and/or the heating tool.
 15. The method of claim 11, wherein the delivery of the alloy beads is achieved via the coiled tubing or pipe that is used to deploy the bridge plug assembly and/or the heating tool.
 16. The method of any one of the preceding claims, further comprising forming one or more openings in the portion of the tubular body wall that is located above the downhole target region and the annular seal.
 17. The method of claim 16, wherein said one or more openings are formed using hole making equipment, wherein the hole making equipment is selected from: a drill, a mechanical punch, a perforating gun, a saw or any other suitable cutting tools such as chemical cutters or fluid jet cutters.
 18. The method of claim 16 or 17, wherein said one or more openings are formed in the tubular body wall before the deflector is positioned within the downhole target region.
 19. The method of any one of the preceding claims, wherein the downhole target region is agitated in order to assist the passage of the alloy beads through said one or more openings into the annulus.
 20. The method of claim 19, wherein the deflector is vibrated to agitate the downhole target region.
 21. The method of claim 19 or 20, wherein the agitation of the downhole target region is achieved by a motor assembly deployed downhole after the deflector has been positioned in the target region.
 22. The method of any one of claims 19 to 21, wherein the tubular body is vibrated to agitate the downhole target region.
 23. The method of any one of the preceding claims, wherein the deflector is deployed downhole in an unexpanded or partially expanded state and then expanded towards the tubular body wall in the downhole target region so as to increase the extent to which the deflector redirects the alloy beads.
 24. The method of any one of the preceding claims, further comprising the intermediate step of retrieving the deflector after the alloy beads have been delivered but before the heating tool is provided within the tubular body and operated.
 25. The method of any one of the preceding claims, further comprising the step of deploying a junk basket downhole via the wellbore tubular body to a position that is down-hole of the downhole target region.
 26. The method of claim 25, wherein the junk basket is delivered downhole either in combination with the bridge plug assembly or the heating tool assembly or on its own.
 27. The method of any one of the preceding claims, wherein the heating tool comprises one or more chemical reaction heaters.
 28. The method of any one of the preceding claims, wherein the alloy beads are provided in the form of a low melting alloy that has melting point of less than 300° C.
 29. The method of any one of the preceding claims, wherein the alloy beads are provided in the form of bismuth based alloy.
 30. A bridge plug assembly for use in forming an alloy plug on an existing annular seal that encircles an oil/gas wellbore tubular body, said assembly comprising: a bridge plug operable to expand against and engage with the wellbore tubular body such that the bridge plug is retained in position within the wellbore tubular body; and a deflector configured to obstruct alloy beads delivered downhole and redirect them radially outwards towards the tubular body wall, wherein the deflector is arranged up-hole of the bridge plug.
 31. The bridge plug assembly of claim 30, further comprising a delivery support connection point, by which the assembly is connectable to delivery means via a delivery support such that said assembly can be delivered to and retrieved from a downhole target region of a wellbore tubular body.
 32. The bridge plug assembly of claim 31, further comprising a delivery support connected to the delivery support connection point and wherein the deflector is located on the delivery support; wherein preferably the delivery support is selected from: coiled tubing, pipe, slick line and wireline.
 33. The bridge plug assembly of claim 30, 31 or 32, wherein the deflector comprises an up-hole facing surface that comprises at least one sloped region.
 34. The bridge plug assembly of claim 30, 31, 32 or 33, wherein the up-hole facing surface of the deflector is cone shaped and preferably the apex of the cone is located at the central axis of the deflector.
 35. The bridge plug assembly of any one of claims 30 to 34, wherein the deflector comprises an agitation mechanism configured to vibrate the deflector.
 36. The bridge plug assembly of any one of claims 30 to 35, wherein the deflector is configured to be expandable radially outwards towards the tubular body wall.
 37. The bridge plug assembly of claim 36, wherein the mechanism by which the expansion of the deflector is achieved is selected from hydraulic means, pneumatic means, mechanical means and combinations thereof.
 38. The assembly of claim 36 or 37, wherein the deflector is urged to expand and/or contract by way of one or more resilient biasing means.
 39. The downhole heater assembly of claim 38, wherein the deflector comprises a canopy of flexible material connected to an umbrella spring mechanism.
 40. The assembly of any one of claims 30 to 39, wherein the deflector comprises insulating means configured to restrict the passage of conducted heat through the deflector.
 41. A downhole heating assembly comprising: a heating tool with at least one heater; a delivery support connection point, by which the heating tool is connectable to delivery means via a delivery support such that said heating assembly can be delivered to and retrieved from a downhole target region of a wellbore tubular body; and a baffle configured to be positionable in the wellbore tubular body at a location between said heating tool and said delivery means, said baffle being configured to restrict the movement of heated fluids produced during the operation of the heating tool.
 42. The downhole heating assembly of claim 41, wherein the baffle is located between the heating tool and the delivery support connection point.
 43. The downhole heater assembly of claim 41 or 42, further comprising a delivery support connected to the delivery support connection point and wherein the baffle is located on the delivery support.
 44. The downhole heater assembly of claim 43, wherein the delivery support is selected from: coiled tubing, pipe, slick line and wireline.
 45. The downhole heater assembly of any one of claims 41 to 44, wherein the baffle is configured to be expandable towards the walls of a wellbore tubular body so as to increase the extent to which the baffle restricts fluid movement within the wellbore.
 46. The downhole heater assembly of claim 45, wherein the mechanism by which the expansion of the baffle is achieved is selected from hydraulic means, pneumatic means, mechanical means and combinations thereof.
 47. The downhole heater assembly of claim 45 or 46, wherein the assembly comprises control means that co-ordinate the operation of the heating tool and the expansion of the baffle.
 48. The downhole heater assembly of any one of claim 45, 46, or 47, wherein the control means that control the expansion of the baffle are provided on the heating tool.
 49. The downhole heater assembly of any one of claims 45 to 48, wherein the baffle is urged to expand and/or contract by way of one or more resilient biasing means.
 50. The downhole heater assembly of claim 49, wherein the baffle comprises a canopy of flexible material connected to an umbrella spring mechanism.
 51. The downhole heater assembly of any one of claims 41 to 50, wherein the baffle is positioned a distance of up to 6 m (approx. 20 feet) from the heating tool, and preferably between 0.3 to 1.0 m (approx. 1 to 3 feet).
 52. The downhole heater assembly of any one of claims 41 to 51, wherein the heating tool comprises one or more chemical reaction heaters.
 53. The downhole heater assembly of any one of claims 41 to 52, the baffle comprises insulating means configured to restrict the passage of conducted heat through the baffle.
 54. The downhole heater assembly of any one of the claims 41 to 53, further comprising a junk basket positioned at the leading end of the assembly. 